Southwest Research Institute (SwRI) has completed development of a spark-ignited hydrogen internal combustion engine designed for medium-duty commercial vehicles.
The two-year development program resulted in an H2-fueled internal combustion engine that SwRI said demonstrates diesel-like torque characteristics and performance while producing near-zero tailpipe CO2 emissions.
The engine was developed in collaboration with a commercial client and selected Tier 1 suppliers. The program included development and testing of both single-cylinder and multi-cylinder engines before the completed engine was designed for installation in a medium-duty commercial truck chassis.
“In addition to decades developing medium- and heavy-duty engines, SwRI has some of the most extensive experience in the world developing and testing H2-ICEs for internal research, clients, and industry demonstrations,” said Dr. Qilong Lu, a program manager in SwRI’s powertrain systems engineering department and one of the leads on this project. “The engine was designed, constructed, and rigorously tested at SwRI to ensure efficiency and performance.”
The H2-ICE is based on a pent-roof-style engine design previously developed for gasoline combustion. SwRI modified the design to optimize it for hydrogen fuel.
Engine development began with work on combustion and injection strategies at the single-cylinder level. The team then transitioned to a multi-cylinder engine while addressing pre-ignition, combustion stability and systems integration.
“We began at the single-cylinder level, focusing on optimizing combustion and injection strategies,” Lu said. “From there, our team ramped up efforts to develop the full multi-cylinder engine, addressing key challenges such as pre-ignition, combustion stability, and overall systems integration.”
The engine uses modified port geometry intended to improve flow and accommodate hydrogen’s faster combustion speeds. A larger intake valve increases volumetric efficiency, while H2-specific fuel injectors are used for hydrogen combustion.
A turbocharger provides diesel-like torque performance, and the engine incorporates an engine control system designed and calibrated by SwRI.
The medium-duty engine is part of SwRI’s broader hydrogen internal combustion engine development work. Previous projects include a Class 8 heavy-duty hydrogen-powered demonstration vehicle and a conversion of a natural gas-fueled engine to an H2-ICE with minimal hardware modifications.
SwRI also previously upgraded an H2-ICE with a state-of-the-art turbocharger to improve performance and make the engine competitive with current long-haul diesel engines, with a focus on fuel economy while maintaining near-zero tailpipe emissions.
“The project brought together many areas and experts at the Institute to complete,” said Chris Bitsis, assistant director of SwRI’s powertrain systems engineering department, who oversees combustion research programs. “SwRI’s hydrogen combustion engine program is working every day to advance this technology and showcase its potential as a near-zero carbon emissions industry solution.”
SwRI maintains a multidisciplinary Hydrogen Energy Research team focused on decarbonization technologies for a range of industries.
Aug 05, 2026
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